Electrical signaling system



8- 1942. R. TAYLOR ETAL 2,292,977 7 ELECTRICAL SIGNALING SYSTEM IOIZOSO 4050 60 7a 0 0 90 0o /ma/ Imalmi h7g4 M45 mad/m M8 was lava/0 LIMA 1111111111 5 Y I wt/ zt/Lij/QLiLjtjyfi zt 264 1 I I I I I I I I I INVENTORS REGINALD TAYLOR GEORGE THOMAS BAKER ATTORNEY Aug. 11,1942.

R. TAYLOR ETAL 2,292,977

ELECTRICAL SIGNALING SYSrfElEi Filed Feb. 24, 1941 4 Sheets-Sheet 2 1 lt'a/ I212? :03 lz'a4 lm5 rad/m7 c08/ca9 00/0 i F L1 1 I 11 1 1 1 1' WU/UYIJJZUI xu y zuZ yu3 Iii-z; 1 1 1 1 1 1 1 1 1 02 M14 103k; yu4 f 1 1 1 1 I I 1' INVENTORS- REGINALD TAYLOR 1 GEORGE THOMAS BAKER ATTORNEY Aug. 11, 1942.

R. TAYLOR ETAL ELECTRICAL SIGNALING SYSTEM Filed Feb. 24, 1941 4 Sheets-Sheet 3 'v ghn .x g m m m w u. 0 I. l|||||||l [IL W IE? m 0 v 9 M M 7 H W m m T 4 5 3 v 9? w E QM n W F INVENTORS REGINALD TAYLOR GEORGE THOMAS BAKER 7 Aug. 11, 1942. R. TAYLOR ETAL ELECTRICAL SIGQALING SYSTEM Filed Feb. 24, 1941 4 Sheets-Sheet 4 INVENTORS REGINALD TAYLOR GEORGE THOMAS- BAKER ATTORNEY Patented Au 11, 1942 ELECTRICAL SIGNALING SYSTEM Reginald Taylor and George Thomas Baker, Liverpool, England, assignors to Associated Telephone & Telegraph Company, Chicago, 111. a corporation of Delaware Application February 24, 1941, Serial No. 380,226 In Great Eritain March 23, 1940 17 Claims.

The present invention concerns improvements in or relating to means for signaling the identity of lines or points over connections of which they form part and while particularly applicable to the identification of calling lines in telephone systems, it will, of course, be understood that it has other applications. Identification of calling lines is required for a number of purposes, one of which is for the automatic recording of calls which are set up, and one application is described for instance in our co-pending application No. 329,608.

The system acordingto the invention is of the type in which each line or point requiring identification over a connection of which it forms part is marked in accordance with a code, as described for instance in our co-pending application No. 321,783. In this prior specification an individual lead was provided from each private wire to one or more bank contacts of a switch which applied the necessary marking to the line for identification purposes.

While this arrangement. was very satisfactory for comparatively small exchanges it tended to involve a rather excessive amount of rotating equipment for larger exchanges, such as exchanges of 10,000 lines, and the object of the present invention is to provide an alternative to the previous arrangement which will in an inexpensive manner and with a minimum of rotating equipment apply marking potentials to a very large number of lines.

Broadly speaking the invention consists of dividing the lines or pointsv of which the identity may be required into a number of different groupings in such a way that no line or point belongs to exactly the same set of groupings as another. For instance in a 10,000 line exchange the lines or points may be divided into different groupings according to those which have the same thousands digit, those which have the same hundreds digit, those which have the same tens digit and those which have the same units digit. It is further necesasry to ensure that there is no conductive connection between different lines or points except when a marking potential is being applied to lines of the same groupings and if the line is used for other purposes such as the private or third wire associated with a calling line then it is important that the potential which may exlet on one Wire for instance a busy potential will not be extended even momentarily to other such wires.

According to one of the. features of the present invention one of the groupings at least is provided with a common lead for each of the groups constituting the grouping, from which common lead connections extend to the individual lines or points of the group and to which common lead momentary connections are made characteristic of the group, such connections to the individual lines or points of the group including means for isolating the individual lines or points from each other during the establishment of the momentary connections by which the individual lines or points of the group are distinguished from each other.

According to a further feature of the invention a relay device, is provided for one at least of said groupings for each of the groups constituting a grouping, which relay device is operated to make a momentary connection characteristic of the group to each line or point of the group. Having regard to economy it is found desirable in a large exchange to make use both of relay devices and static devices which are conductive when used for characterising signals and substantially insulating for other electrical conditions to which they may be subject, for instance the static devices may take the form of condensers or nonlinear resistance devices, such as being formed of a material consisting of a mixture of silicon carbide and carbon and/or tungsten or molybdenum which is agglomerated under pressure and subsequently baked. This latter device has the advantage of having normally a high resistance and therefor serving to substantially insulate a line while when a high voltage is applied thereto the resistance falls sufficiently to allow signaling currents to flow to the line.

According to a further feature of the invention in an arrangement for signaling the identity oflines or points over the connections of which they form part, in which a plurality of said lines or points are commoned in a group and the common leadis provided for group identification over which characterising signals are simultaneously impresesd on all lines forming such group, static devices are employed which are conductive When used for the characterising signals and substantially insulating for other electrical conditions to which the lines or points may be subject and serve for the transmission of signals from the common lead to the individual lines or points.

In a preferred form of the invention two such static devices are provided per line, one connected between the line and a common leadto which similar devices connected to other lines having the same thousands and the same tens digit are connected, while the other impedance device is connected to a common lead to which other devices associated with lines having the same hundreds and units digits are connected. A relay device is provided for connecting to all common leads associated with lines having the same thousand digit marking potentials at particular instants of time in the cycle determined by a rotary switching device or its equivalent. A similar relay device is provided to connect up to all the common leads associated with lines having the same hundreds digit marking potentials at particular instants of time in the cycle determined as before mentioned. There are therefore ten relay devices provided for each grouping. These relay devices in operating serve to isolate the common leads from other common leads to which potentials are applied corresponding to the various tens digits and units digits respectively. By allocating five contacts of a uni-selector switch for each digit it is possible to so control the pulses applied to the whole of the 10,000 lines that to each line there are two impulses for each digit selected out of a possible five pulses to characterise the particular digit to be transmitted. The receiving switch which operates in synchronism with the marking control switch is then able to select various relay combinations corresponding to the number of the line to be identified, provided of course that it operates in synchronism in the manner described in our prior application No. 321,783.

The invention will be better understood from the following description of one method of carrying it into efiect, reference being had to the accompanying drawings comprising Figs. 1-4 which usual type of register translator exchange numshould be arranged in the manner shown in Fig. ber comprising three letters and four numerical 2, whereupon Figs. 1 and 2 will show line markdigits, y for instance HOLbOIII 35, which may ing equipment suitable for an exchange of up to be anscr b d 4 118 Seve group of fi e 10,000 subscribers, numbered from 1111-0000, pulses each will be transmitted to the outEOi g while Figs. 3 and 4 will show marking control relay set and stored y means f Selections f equipment for association with the line marking Seven pa e t r y-fiv consecutive p s of equipment of Figs. 1 and 2. As cases often arise the regenerater- AS the first p Of the in which the subscribers numbers are prefixed by her is t e for a l ubscr be s On t e eX- a digit, digits, code letter, or code letters com- Change, it is ng d that this shall be common to all the subscribers on an exchange, the mllnieated direct from e marking C t 0 marking control equipment is also adapted to equipment v Common leads to the t g provide for the marking of the common prefix or relay set without involving transmission over the digits in addition to controlling the marking of l ng train pr v ondu or as in the case of the numerical portions of the subscribers numthe numerical portion of the subscribers numb her which is different for each subscriber on the Before proceeding with the circuit operations exchange.

involved in marking the various private leads as- The seven groups of five pulses forming the sociated with each line in an exchange with codes code signal train required to signal the identity indicative thereof, a general consideration will of the calling subscribers number HOL 1185 may first be given to the type of code utilised, and be indicated in the following manner, the markalso to a suitable method of storage at the ing pulses being indicated by the relevant letter originating exchange if this be required. and the spacing pulses by a dash.

Pulses 1 6 11 1c 21 2e 31 35 Signals v---z ---YZ -WX-- VW--- vi --XY- -wx-- Digits 4 0 5 1 1 s 5 As regards the code employed, this is prefer- Thirty-five code signals will be received by the ably of the well-known five unit type in which outgoing relay set and pairs of regenerator pins every digit consists of five parts and by sending corresponding to the various marking pulses for special signals in one or more of these parts the each digit are displaced in an arc of thirty-five various digits are indicated; parts or units withconsecutive pins thereon, and in this manner the out a special signal are known as spacing pulse, subscribers number can be stored in code by and those with a special signal, marking pulses. means of displaced pins. In the five unit code every digit comprises two Consideration will now be given to a preferred marking pulses and three spacing pulses, and it is method according to the invention for extending arranged that the special signal characteristic of marking signals on to the test conductors of the a marking pulse comprises a pulse which is transvarious subscribers on a 10,000 line exchange and mitted along the private lead to an outgoing refor this purpose reference should be had to the lay set at the originating exchange where the line marking equipment of Figs. 1 and 2 in which calling number is usually stored. For a spacing the arrangements are such as to utilise per expulse no such signal is transmitted but it will be understood that both marking and spacing pulses involve the transmission of synchronising pulses which are supplied independently of the talking train and over a common lead from the marking control equipment to the outgoing relay set.

Assuming for instance that the five parts of the code are designated V, W, X, Y, Z, respectively, the various digits will be transmitted by sending marking pulses in the parts indicated in the following table:

For a four digit number a total of four groups of five pulses each will be transmitted to the outgoing relay set and if storage is required this may be effected on an impulse storage and regenerative device of the type described in United States Patent No. 2,188,451, and in the manner disclosed in our co-pending application, No. 329,608, in which the outgoing relay set described is adapted to operate with identification equipment of the type according to the present invention. The four digit number is thereupon stored in the same five unit code as received, a set of five pins in sequence on the regenerator forming each digit, and two selected pins in each of these groups of five being displaced in accordance with the particular digit involved.

Assuming that the calling subscriber has the change a small number of code marking relays and group switching relays Whicharecontrolled from a stepping .switch and which operate in conjunction With two static connecting or .commoning devices per test conductor; it'being believed that this combination involves the "minimum amount of moving apparatus consistent with cheapness, although as will be described later, the Whole scheme can be rendered almost completely static, if desired-by the use of more than two static connecting devices per line.

The expression static connecting device is employed to cover any device which is normally an insulator or substantially so and is adapted to become conducting with appropriate changes applied thereto such as changes of voltage without necessitating the movement of any external member asso iated therewith.

The exchange is assumed to be of the rotary line switch type and it will be understood that the test wire of each subscriber is connected via static connecting devices such as SCD'I and SCD2 to two common leads extending from the line marking equipment, the connections for subscriber No. 1185 being showninthe drawings.

The devices SCDI of each subscriber having the same tens digit in each 100 line group are commoned together so-that the 1 00 devices such as SCDI are connected to ten common leads. These common leads from each 100 line group having the same thousands digit are in turn commoned together so that for each of the different thousands digits in the exchange there willbe ten common leads (corresponding to the various tens digits 14)), which respectively extend to ten armatures of a thousands group switching relay such as yl MA, (relays IMA, ZMA bein provided for the various 1,000 line groups) Over operated armatures of reach of these re-- lays marking signals characteristic of the various thousands groups are communicated via the devices suchasSQDl to the subscribers test conductors. The resting ,armatures .of these relays 1. 61 over ten common leads to armatures of five tens code marking relays N'l -ZT by'means of which marking signals indicative of the tens digits of .the various subscribers numbers are transmitted through to the test conductors.

Hence on this side of the circuit the thousands and tens digits of the various numbers on the exchange can be determined,

Devices SCDZ of each subscriber having the same units digit in a 100 line group are commoned together so that the 100 devices are connected to ten common leads and common leads having the same hundreds digit are in turn commoned for all 100 line groups.

For each of the different hundreds digits of the exchange numbering scheme, relays ICA, ZCA are provided and to the ten armatures of each of these relays extend ten common leads from the subscribers in the groups having the relevant hundreds digit.

Over operated armatures if the relays ICA, ZCA marking signals characteristic of the hundreds digits of the various subscribers on the exchange are extended through to the test conductors, while the resting armatures connect with armatures of units digits code marking relays W to ZU by means of which marking signals characteristic of the units digits of the subscribers numbers are extended to line.

Alternating current code signals are employed in order that connection of the signal receiving device at, for instance, the outgoing relay set,

may be made to the test conductor without interfering with the direct current guarding, holding and signaling potentials which may be present thereon. Furthermore in order that the test conductors may :be connected together and that connection may be made thereto from the line markingeouipment without causing interference, the two connections from the line marking equipment toieach test lead are made via the connecting devices SCDI and SCDZ which may each comprise a condenser which would allow alternating current to pass therethrough and which would at the same time isolate the circuit against a flow of direct current to or from the P conductor. Alternatively, use might be made of a multi-electrode neon tube which would have one central common electrode surrounded by say ten individual electrodes all of which would break down when a marking signal was applied to provide a common connection to ten P conductors.

A cheap, efiicient, and generally preferred form of connecting device which is assumed to be utilised in Fig. 1 consists of a unit of non-linear resistance material which is substantially an insulator when the voltage across it is the normal exchange battery potential of fifty volts, but the resistance of which decreases considerably with an applied signal voltage having a value greater than fifty volts.

A preferred example of this material is a mixture of silicon carbide with carbon and/or tungsten or molybdenum which is agglomerated under pressure and subsequently baked. The material is conveniently made up in the form of discs about the size of a shilling, and the flat surfaces sufliciently to give a satisfactory contact. The

discs could if desired be separate, but the combined arrangement is more convenient.

In the case where the connecting devices SCDI and SCDZ comprise, non-linear resistance discs,

the various common leads to which the discs are connected asshown in Figs. 1 and 2, are normally connected to the negative side of the exchange battery in order to prevent possible back feed trouble in the case where for example the majority of the private conductors are earthed and the minority are not earthed, in which case it might be possible to hold operated the cut-off relays connected to the latter P conductors were it not for the negative battery connected to the common lead which provides an effective short circuit for said relays; Owing to the non-linear characteristic of the discs, the current drain on busy lines, the test conductors of which are earthed, will be almost negligible, while the current drain on free lines will be zero.

Signaling the identification of calling lines is performed by injecting an AC signaling voltage into the battery connected common. leads whereupon since it will be understood that lines requiring identification will have connected thereto, at the outgoing relay set or other place where the identification, is required, a responding relay which is earthed via a condenser to prevent normal direct current flow, a voltage considerably greater than the normal battery voltage will be applied across the various discs during half cycles of applied A. C. voltage which assist the battery voltage. These discs thereby break down and allow current to flow therethrough, thereby allowing signals to be extended to line and thence to the various responding relays which will now operate. In order to prevent the busying earths on the various P conductors from short circuiting the various responding relays it will be arranged that the busying earths which will be applied to the P leads during identification will be extended via suitable small chokes which serve to offer a relatively high impedance to the signaling currents but which have a low direct current resistance so as not to interfere with the guarding arrangements.

Itmay be mentioned here that the use of non-linear resistance units instead of condensers as static connecting means gives an advantage as regards the amount of operating power which can be delivered to line. With non-linear resistance units, only those units in circuit between the common signaling point and the P conductors will be caused to lower their resistances when the A. C. signaling voltage is applied while the other unit of the pair in each case maintains its normal high resistance and so do not offer any serious leakage shunt path as is the case with condensers, the impedance of which does not alter with variation in voltage. The use of non-linear resistance units therefore enables a given power output to be delivered to line with a minimum wastage of power in shunt paths.

For the purpose of explaining the identification equipment circuits, it will be assumed that a calling subscriber is on a register-translator exchange, and has the number HOLborn 1185, and that he sets up automatically a call to an exchange outside the area, which call will require to be automatically recorded.

The outgoing relay set at the originating exchange is adapted on being taken into use to set in operation identification equipment which thereupon communicates details of the calling number thereto. This number is stored until information as to the identification of the calling party is required by the exchange at which the toll recording equipment is situated.

In some cases, for instance, in the case of a call to a manual board, it may prove more desirable not to store the information in the outgoing relay set, and the identification equipment in this instance is not started up until a signal transmitted back from the operators position is received at the outgoing relay set. Owing to the speed at which the system according to the invention can identify a calling line, it is particularly applicable to requirements of this nature.

In the former case it is generally arranged that as soon as the outgoing relay set is taken into use, if the identification or line marking equipment is not already in operation as is indicated by the presence of an earth potential on common lead S (Fig. 4) which in conjunction with the other common leads STZ (Figs. 3 and 4), connects with the various exchange outgoing relay sets, then earth will be extended from the outgoing relay set on to the common lead ST. Relay STR (Fig; 3) thereupon operate's and at armature strl removes the short circuit from relay SSR previously extended from earth on wiper MSI of the reverse drive stepby-st'ep marking switch MS in its home position S to earth over armature szrl. Relay SSR. in operating connects earth up to relay IGR (Fig. 4). The operation of relay IGR, is dependent on the open condition of impulse springs IPB which are continuously operated in synchronism with springs IPA at a rate of about ten impulses per second, and as soon as these springs open after having been closed, relay IGR operates and at armature z'grl connects springs IPB up to magnet MSM of the switch MS while at armature i913 earth is extended to springs IPA which connect up with the pulse lead PU extending to the outgoing junction relay set, over which lead the synchronizing pulses are extended.

It will be remembered that the code signals indicative of the initial digits HOL, which might be transcribed 405, of the calling number, are extended direct from the marking control equipment to the outgoing relay set, as these digits are the same for all subscribers on the originating exchange, and the extension of these signals in five unit code form is effected in the following manner.

Contacts 2I6 of the MS switch bank MS] are allocated for this purpose, these contacts being divided up into three groups of five contacts each, and being strapped to relay ECR in accordance with the particular marking signals to be transmitted for the code 405. For this code it will be remembered that pulses Nos. I and 5, 9 and It], I2 and I3, will have to be marking pulses so that corresponding contacts 2, 6, I8, ll, I3 and M on bank MS! will be strapped to relay ECR.

On the next closure of the impulse springs IPA and IPB, earth will be extended over the PU lead to energise the reverse drive receiving magnet of the regenerator in the outgoing relay set, while at the'same time impulsing springs IPB will energise the reverse drive marking switch magnet MSM. On the next opening of these contacts the regenerator receiving magnet and magnet MSM are de-energised and the former advances the mechanism one step to a position opposite the first of the row of pins required for storing the calling number while the latter advances its wipers one step to position 2.

It is now necessar to send a marking pulse to the outgoing relay set and it will be seen that wiper MSI will extend an earth to operate relay ECR which thereupon at armature ecrl (Fig. 4) connects a commercial 50 cycle frequency alternating current source via transformer TRA on to the exchange code common lead EC extending to the outgoing relay set; lead EC is common to the various outgoing relay sets in the same way as the already mentioned common leads ST-Z. It will be understood that as a result a sensitive relay in the outgoing relay set which is responsive to alternating current and which is also connected to the test lead for the purpose of responding to marking signals received over the P conductor is operated to bring about a mechanical marking of the alternating current marking pulse on the regenerator by pin displacement in the manner described in the previously mentioned application No. 329,608.

The next closure and subsequent opening of the impulse springs IPA and IPB advance the regenerator mechanism and the switch MS a further step and in this position of switch MS it will be seen that relay ECR is not operated, so that no marking pulse is transmitted over the exchange common lead EC to displace a pin in the regenerator, and this pulse therefore constitutes a spacing pulse.

Marking and spacing signals are transmitted in this manner to set up the code indicative of the prefix portion of the calling number on the outgoing relay set regenerator.

The marking switch wipers on reaching position I! commence to signal the numerical portion H85 of the calling subscribers number. As before the spacing signals simply comprise pulses delivered directly to the outgoing relay set regenerator over the PU lead, but now the marking pulses comprise pulses delivered simultaneously over the PU lead and via the line marking equipment of Figs. 1 and, 2 to the private leads of the various subscribers on the exchange, from whence they may extend via connections already set up to outgoing relay sets.

Marking signals characteristic of these four digits are distributed from the banks MSl-MSB (Figs. 3 and 4) of switch MS, which banks are wired up as shown to four groups of leads extending to the linemarking equipment (Figs. 1 and 2) the groups TH, HU, TE and UN, serving the thousands, hundreds, tens and units digits respectively.

Ihe connections from the banks MS l' MS 3 to these leads will be better appreciated by considering the signaling of the digit 1185 of the calling subscribers number referred to, and for this purpose it will be remembered that pulses Nos. I6 and H, 2!- and 22, '23 and 23, 32 and 33 in the complete train. of thirty-five pulses which is sent will have to be marking impulses.

Hence when the switch wipers are advanced to contact 11 corresponding to signaling pulse N0. IE, it will be necessary to extend a pulse on to the P conductor of the calling subscriber in question, and this is effected by the extension of earth over wiper M Sl in position H and TH group lead I to operate the thousandsgroup switching relay IMA (Fig. 1) in the line marking equipment. This relay in operating connects the common lead AC, on to which alternating current is con. tinuously impressed via the transformer TRA in Fig. 4, to the. non-linear resistance disc corresponding to discSCDt of every subscriber whose number commences with the thousands digit 1. These discs thereuponbecome of low resistance. In the present instance the disc SCDI associated with subscriber No. 1185 in breaking down will allow the marking signal to extend to the out.- going relay set where it operates the signal respending relay to cause the regenerator marking magnet to operate and by displacing a pin to store the signal on the regenerator. This will apply to all the above-mentioned subscribers lines from which calls have been set up to outgoing relay sets while in the case of other lines having the thousands digit 1 and from which such calls have not been setup the signals will not be made use of.

In position I! of the marking switch MS the leads 2, 3, 4 of the thousands group TH are also earthed over wipers and banks M85, M83 and MS! respectively, and the respective group switching relays ZMA, 3MA and 4MA are operated to extend a marking signal on to the test conductors of all subscribers on the exchange having the thousands digit 2, 3 or 4' as. all. these digits have in their code designations. the same initial pulse.

When the wipers are advanced to position l8, lead No. I; in the group TH is earthed over wiper and bank MS'I so as to extend asecond marking pulse over the P conductors of subscribers having at thousands digit 1. At the same time TH group lead No. 5 is earthed over wiper and bank MS3 for the purpose of extending the first marking signal characteristic of the thousands digit 5 over the P conductorsof subscribers having a thousands digit 5, while leads 6 and l in group TH are earthed over wiper and banks M and MS! for the same purpose in connection with subscribers having thousands digits 6 and 7 which digits 5, 6 and 7 have code designations in which a pulse occurs in the second position of the cycle.

With the MS switch wipers in positions I9, 20 and 2|, no further marking pulses are delivered to. the P conductors of those subscribers having the thousands digit 1, but marking signals will be delivered in these positions of the wipers to P conductors of subscribers having other thousands digits for similar reasons as those stated above and in a manner which can be appreciated from examination of the connections.

With the MS switch wipers in positions 2 2-26 marking signals characteristic of the hundreds digits of the various subscribers on the'exchange are delivered via the leads l!] of the hundreds group EU in the manner already described in connection with the thousands group leads TH, the only difference being that in this instance the hundreds group switching relays ICA, ZCA are brought into operation and con nect up the alternating current source over lead AC via the non-linear resistance discs such as SCDZ to the subscribers test conductors.

For the purpose of extending marking signals to line indicative of the tens and units digits of the subscribers numbers, wiper and bank M38 is utilized which connects up with five coding leads V, W, X, Y, Z'in turn in the tens'and units groups TE and UN so as differentiall-y'to operate the tens and units coding relays VT--,ZT, VU-- ZU and so effect the markings;

In the present instance where the tens and units digits of the calling number are 85, it will be seen that an alternating current impulse is extended to line when relays XT and YT are. operated which means that pulses Nos. 28. and 29, 32 and 33 in the train of thirty-five pulses are marking pulses, and in the corresponding positions 29 and 30, 33 and 34 of the MS switch, it will be seen that relays XT and YT, WU and XU are operated.

When the MS switch advances to contact. 31: the complete train of thirty-five impulses constituting fourteen marking and twenty-one spacing pulses positioned in accordance with the calling number in question, will have been transmitted to the outgoing relay set and earth is now extended over wiper and bank MS}; to bring'up, relay SZR which in operating at armature szrl releases relays SSR and IGR in turn and at armature igrl the impulsing circuit to the magnet MSM is opened. The earth potential normally extended on to the Z'lead connecting with the outgoing relay set is also removed by armature $213, so as to signal that the end of the cycle has been reached. At the same time a self-interrupted driving circuit is completed for the magnet 'MSM over armature szrll and the wipers are quickly rotated through to the home position I where the driving circuit is opened. When this position is reached relay SZR restores to normal and in so doing at armature szr3 replaces the earth on the Z lead, reprepares an operating circuit for relay SSE at armature szrl and at armature 'szrZ applies earth on to lead S extending to the various outgoing relay sets so as to signal to these relay sets that the identification equipment is in its home position in readiness for operating through a further complete cycle when required.

In the arrangement described the same alternating current frequency has been used for sending both marking and spacing signals, and this has been possible by virtue of the use of two signaling channels. For the purpose of communicating the stored calling number in the outgoing relay set regenerator to the exchange where the call recording equipment is located, however, it will be preferable to utilise two difierent types of signals, since only the junction line is available for signaling. In this case it is proposed to use for spacing signals the same 50 cycle mains frequency, but for marking signals a combination of the 50 cycle frequency with a 150 cycle frequency will be transmitted. This combination signal can be supplied from the marking control unit of Figs. 3 and 4 where it is derived from the common 50 cycle source in the simple manner shown in Fig. 3. A non-linear resistance disc NLRI of the same type as is used for connecting devices SCDI and SCDZ is connected in series with the primary winding of the transformer TRB and the 50 cycle source is connected up as shown. As a result the output in the secondary winding of this transformer will contain a. large third harmonic component, i. e. 150 cycles, and the combined 50 plus 150 cycle output obtained in the secondary winding is thereupon supplied over a common lead to the various out-1 going relay sets.

The relative strengths of the 50 cycle and 150 cycle frequencies in the output circuit are adjustto start up the identification in response to a signal from the toll recording exchange, the marking signals received over either the P conductor and the PU lead or the EC lead and the PU lead from the identification equipment will be converted at the outgoing relay set into 150 plus 50 cycle signals before being extended out on to the junction line to the toll recording exchange, while spacing signals which will be received from the identification equipment over lead PU only will be transmitted to line as 50 cycle signals. For this latter purpose a. 50 cycle supply is made available to the various outgoing relay sets from the marking control relay set.

The invention is not limited to the precise line marking arrangement described, and the equipment could be made almost completely static in operation by using say four static connecting devices per line in the case of a 10,000 line exchange.

- It is believed however, that the arrangement described in which two devices are provided per line and are operated in conjunction with a small number of group switching relays, provides the most economical form of identification equipment employing a small number of moving parts.

In the case of register translator areas, where code letters prefix the four digit subscribers numbers, and where a number of central exchanges at which are located call recording equipment each serve a number of ordinary exchanges, then it is not essential to transmit code signals directly indicative of the code letters of a calling number to a central exchange in View of the fact that since only a small group of exchanges out of the total area will be operated into each central exchange, one digit or at the most, two digits, could be transmitted forward to the central exchange to identify the particular exchange in the group which is calling.

In the case where several calling equipments require the same number marking such as obtains with P. B, X lines, then each of these lines will be dealt with as a separate line, and will be provided with two static connecting devices. The centre tapped sides of these devices will be Wired out to the various P conductor of the P. B. X group, while the other sides thereof may be wired out to the same common points, so as to receive the same markings. Further consideration of this feature is given in British application No. 9886/40.

From the foregoing description it will be seen that the invention provides an extremely eificient method of line or point identification owing to the use of so few moving parts, while at the same time the cost per line is small.

We claim:

1. In a telephone system, a plurality of subscriber lines arbitrarily divided into a plurality of primary groups and a plurality of secondary groups so that each line belongs to a particular primary group and also to a particular secondary group and so that none of th lines belonging to the same primary group belong to the same secondary group and none of the lines belOnging to the same secondary group belong to the same primary group, a different signal input for each of said groups, means permanently connecting each of said lines to the signal input for the primary group to which that line belongs, means also permanently connecting each of said lines to the signal input for the secondary group to which that line belongs, and mean associated with each input for impressing upon all lines connected thereto a signal characteristic of the group corresponding to that input, whereby each of said lines has impressed upon it signals characteristic of both groups to which it belongs.

2. In a system as claimed in claim 1, means in the connection extending from each line to one signal input for preventing a signal impressed upon that line from the other input to which said line is connected from being transmitted to said one input over said connection extending thereto.

3. In a telephone system, a plurality of subscribers lines arbitrarily divided into a plurality of primary groups and a plurality of secondary groups so that each line belongs to a particular primary group and also to a particular secondary group and so that none of the lines belonging to the same primary group belong to the same secondary group and none of the lines belonging to the same secondary group belong to the same primary group, a different signal input for each of said primary groups, means permanently connecting each of said lines to the signal input for the primary group to which that line belongs, means associated with each signal input for impressing upon all lines connected thereto a signal characteristic of the primary group corresponding to that input, and means for also impressing up each of said lines a signal characteristic of the secondary group to which that line belongs.

4. A telephone system as claimed in claim 3,

whereineach of said subscribers lines has different values of direct current potential impressed upon it at difierent times, and wherein the means connecting each of said lines to a signal input includes a device for preventing the directicurrent potential present on that line from manifesting itself at said signal input.

5. In a telephone system, a plurality of subscribers lines arbitrarily divided into a plurality of primary groups and a plurality of secondary groups so that each line belongs to a particular primary group and also to aparticular secondary group and so that none of the lines belonging to the same primary group belong to the same secondary group and none ofthe lines belonging to .the sam secondary group belong to the same primary group, a different signal input for each of said primary groups, a permanent connection extending from each of said lines to the signal input for the primary group to which that line belongs, means associated with each signal input for impressing upon all of said lines connected thereto a signal characteristic of the primary group corresponding to that input, means for also impressing upon each of said lines a signal characteristic of the secondary group to which that line belongs, and means in each said permanent connection between a signal input and a subscribers line for preventing the signal characteristic of the secondary group to which that line belongs, when impressed upon said line, from passing over said connection to said signal input, whereby no line can receive over its connection to a particular signal input the signal characteristic of a secondary group which is impressed upon any other line connected to. the same signal input.

6. A system as claimed in claim 5, wherein said last means comprises a non-linear resistance having a high resistance when a low voltage is impressed upon it and a lower resistance when a higher voltage is impressed upon it.

'7. In a telephone system, a plurality of subscribers lines arbitrarily divided into a plurality of primary groups and a plurality of secondary groups so that each line, belongs to a particular primary group and also to a particular secondary group and so that none of the lines belonging to the same primary group belong to the same secondary group and none of the lines belonging to the same secondary group belong to the same primary group, a static resistor associated with each of said subscribers lines, a different signal input for each primary group of lines, means permanently connecting each of said lines via its associated resistor to the signal input for the primary group to which that line belongs, said resistors having a non-linear resistance characteristic and, in the absence of a signal in the sign-a1 input to which they are connected, being of such resistance as to substantially insulate irom one another the subscribers lines connected to that signal input, means for generating in each signal input a signal characteristic of the primary group corresponding to that input, said signal effective to render the static resistors connected to that input conductive whereby said signal is impressed upon all of the subscribers lines connected to said input, and means for also impressing upon each of said subscribers lines a signal characteristic of the secondary group to which that line belongs.

8. In a telephone system, a plurality of subscribers lines arbitrarily divided into a plurality of primary groups and a plurality of secondary groups so that each line belongs to a particular primary group and also to a particular secondary group and so that none of the lines belonging to the same primary group belong to the same secondary group and none of the lines belonging to the same secondary group belong to the same primary group, two static resistors associated with each of said subscribers lines, a different signal input for each of said groups, means permanently connecting each of said lines via one of its associated resistors to the signal input for the primary groups to which that line belongs, means permanently connecting each of said lines via the other of its associated resistors to the signal input for the secondary group to which that line belongs, said resistors having a nonlinear resistance characteristic and, in the absence of a signal in the signal input to which they are connected, being of such resistance as to substantially insulate from one another the subscribers lines connected to that signal input, means for generating in each signal input a signal characteristic of the group corresponding to that input, said signal effective to render the static resistors connected to that input conductive, whereby the signal characteristic of each input is impressed via said resistors to all of the subscribers lines connected to said input.

9. In a telephone system, a plurality of subscribers lines arbitrarily divided into a plurality of primary groups and a plurality of secondary groups so that each line belongs to a particular primary group and also to a particular secondary group and so that none of the lines belonging to the same primary group belong to the same secondary group and none of the lines belonging to the same secondary group belong to the same primary group, means associated with each primary group effective normally to connect in multiple all subscribers lines belonging to that group whether those lines individually are idle or engaged in calls, means for at times impressing upon the lines of each primary group over the multiple connection to those lines a signal characteristic of that primary group, means for at other times impressing upon each of said lines a sign-a1 characteristic of the secondary group to which that line belongs, and means operated to interrupt said multiple connections at said other times to prevent any line from receiving over said multiple connection the signal impressed at said other times upon any other line belonging to the same primary group as that line.

10. In a telephone system wherein a plurality of subscribers lines terminate in the same exchange, and wherein each of said lines has different values of direct current potential impressed upon it at different times, whereby a difference of potential sometimes exists between different ones of said lines at said exchange, a network of cross connections at said exchange,

said network including a permanent connection from each of said lines to every other one of said lines, and means in the connection between each pair of lines for preventing the direct current potential present upon one line of said pair from manifesting itself upon the other line of said pair.

11. In a telephone system wherein a plurality of subscribers lines terminate in the same exchange, and wherein each of said lines has differincluding a permanent connection from each of said lines to every other one of said lines, a static resistor in the connection between each pair of lines, said resistor having an inverse non-linear resistance characteristic and acting substantially as an insulator in the presence of said potential difference sometimes existing between said pair of lines, and means for at times impressing another potential upon said resistor to cause it to become conductive.

12. In a telephone system wherein a plurality of subscribers lines terminate in the same exchange, and wherein each of said lines has different values of direct current potential impressed upon it at different times, whereby a difference of potential sometimes exists between different ones of said lines at said exchange, a line at the exchange common to all of said subscribers lines, a permanent connection from each of said subscribers lines to said common line, a static resistor in each said connection, said resistor having an inverse non-linear resistance characteristic and acting substantially as an insulator in the presence of potential of the value of said potentials impressed upon said subscribers lines, whereby the direct current potential on any of said subscribers lines cannot manifest itself on any other subscribers line over the connections of those two subscribers lines to said common line, and means for at times impressing upon said common line a potential of such value as to cause said resistors to become conductive.

13. In a telephone system wherein a plurality of subscribers lines terminate in the same exchange, and wherein each of said lines has different values of direct current potential impressed upon it at different times, whereby a difference 14. In a telephone system, a plurality of subscribers lines each characterized in one Way when it is idle and in a different way when it is engaged in a call, means normally connecting said lines in multiple regardless of whether said lines individually are idle or engaged in calls, and means in said multiple connection for preventing the way in which any line is characterized from being manifest, over said multiple connection, at any other line.

15. In a telephone system, a plurality of subscribers lines, each characterized in one Way when it is idle and in a different way when it is engaged in a call, a static device for each of said lines, a junction point common to all of said lines, means normally connecting each of said lines via its static device to said common point regardless of whether that line is idle or engaged in a call, each of said devices effective to prevent the way in which its associated line is characterized from being manifest at said common point.

16. In a telephone system, a plurality of subscribers lines, each characterized in one Way when it is idle and in a different way when it is engaged in a call, a static device for each of said lines, a junction point common to all of said lines, means normally connecting each of said lines via its static device to said common point regardless of Whether that line is idle or engaged in a call, each of said devices effective to prevent the way in which its associated line is characterized from being manifest at said common point, means for impressing a signal upon said common point, each of said devices effective to conduct said signal to its associated subscribers line.

1'7. In a telephone system, a plurality of groups of subscribers lines, a common lead for each said group, means permanently connecting each of said lines to the common lead for the group to which that line belongs, means effective to divide said common leads into groups in different ways at different times so that common leads belonging to the same group at one time will belong to difierent groups at another time, and means for impressing upon said common leads at each of said times a signal characteristic of the group to which that lead belongs at that time.

REGINALD TAYLOR. GEORGE THOMAS BAKER. 

